DE1938746A1 - Compensation circuit for series servo motor - Google Patents

Description

Patent attorney DipL-Phys. Gerhard Liedl 8 iünchen 22 Steinsdorfstr. 21-22 Tel. 29 84

B 4305

TOKYO ELECTRICAL ENGINEERING COLLEGE No. 2-2, Kandanishiki-cho, Chiyoda-ku, Tokyo / JAPAN

and

TADAO FUJIMAKI No. 6 -15 - 25 ,. Sakuradai, Nerima-ku, Tokyo / JAPAN

Compensation circuit for series servo motor

The invention relates to a compensation circuit for a series servo motor to improve the start-up characteristics,

DC motors in series have a high starting torque

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and constant performance. A well-known control servo with this characteristic is used in the form of a two-field servo motor. However, this engine is on a small size limited. The presence of the ineffective range of the given voltage-speed characteristic of a servomotor in which this does not respond and which can be traced back to the brush friction and the like, has, viewed as a whole, a very disadvantageous effect the characteristics of the servo system. So far there are no suggestions for Elimination of these disadvantages has been made.

It is therefore the object of the present invention to propose a compensation circuit by means of which the ineffective area the voltage-speed characteristic of a direct current series servo motor and the motor can be switched so that it works as a shunt motor when the control voltage is low and as a series motor when the control voltage is increased. This task will solved in that the field winding of the motor on the DC side a rectifier bridge circuit with a compensation current source is connected so that a constant current flows in the field winding, and that the armature of the motor is in series with the AC side the rectifier bridge circuit is connected and forms a series circuit to which a control voltage is applied.

An embodiment of the present invention will be described below of the accompanying drawings explained in more detail.

Show it:

Fig. 1 is a circuit diagram of a first embodiment of the invention Circuit;

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FIG. 2 partial circuit diagrams ^{to explain the 3} circuit diagram shown in FIG. 1; FIG.

4 shows partial circuit diagrams of further embodiments of the invention; until 6

7 shows a voltage characteristic when starting without a load;

8 shows a voltage-speed characteristic of the invention Switching system;

9 shows a speed-torque characteristic of the invention Switching system and

Fig. 10 shows the step response characteristics of the present invention Switching system.

In Fig. 1, 1 denotes a rectifying bridge circuit which consists of rectifying elements D / to D. Another rectification -

1 4

Bridge circuit 2 consists of rectifying elements D 'to D', both Rectifying circuits 1 and 2 are coupled in series on their DC side or at points P and Q 'and form a series circuit, the with a field winding 6 of a direct current series servo motor connected at opposite points Q and P '. The armature 7 of the direct current series current servomotor is in series with the rectifying bridge circuit 1 on their alternating current side or at points R and S in connection. Connections 4 and 5 connect to this series connection a control voltage e applied. A Kompensatioißäzanqde applies a compensation voltage to the connection points R 'and S' on the

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AC side of the second bridge circuit 2. The power source 3 can be a direct current or alternating current source. If a suitable one The value of the compensation voltage e> in accordance with the Capacity of the servomotor is selected, a compensation current flows (Field current) if of constant direction during the whole Time in the field winding 6. This compensation current if causes a continuous induced magnetic flux in the field winding

The torque of a servo motor is to see the product of the magnetic flux W and the armature current proportional. Therefore, when the control voltage e is gradually increased from zero, the servomotor starts up even if the control voltage is relatively low, since magnetic flux is induced in the field winding due to the compensation current. The servo motor works in two different ways, depending on the circuit constants, the load, the compensation current and the control voltage.

One mode of operation is that all rectifying elements D _{1 to D 4 of} the bridge circuit 1 fire, while the other mode of operation consists in that only the two opposing rectifier elements D 1 and D _{1 or D 1 and D 4 of} the bridge circuit 1 fire.

The servomotor exhibits a bypass characteristic when Hal if, and it shows series connection characteristics when lial = if, where ia der Aiterkstrom and if is the magnetic field current. This will follow in the * explained in more detail.

Assume that the control voltage e is zero and the compensation voltage e 'is applied in such a way that R' is on the positive side, then the compensation voltage e 'causes a direction of compensation -

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Current if in the direction of the solid arrow in Fig. 2 to the field winding 6 as field current. The stream is divided into two partial streams if / 2, each of which flows to the elements D ", D", D "and D. and she ignites. The potential differences between points P and Q (on the direct current side) and between points R and S (on the alternating current side) are zero. If the resistances of the rectifying elements D- to D. and D'- to D *, in the forward direction and thus a, If the voltage drop in this direction is neglected, the compensation voltage lies e 'at the opposite ends of the field winding. In this case, the control voltage e between the terminals 4 and 5 applied so that the terminal 4 on the opposite side lies. At this time, the current ia flows into the dash-dotted line in FIG indicated direction. However, when the control voltage e is relatively low and the current ia is lower than the compensation current if, is the current flowing to the field winding 6 is necessarily limited to the constant current if, which is due to the impedance of the field circuit and the Compensation voltage e 'is effected so that the current ia to the armature 7 flows. The impedance of the field circuit is equal to the impedance of the Field winding because, as mentioned, the resistances of the rectifying elements can be neglected in the forward direction.

Since the current if flows to the field winding 6 and the current ia to the armature 7, apply to the bridge circuit using Kirchiioff's laws 1 and the current directions given in Fig. 3 use the following equations:

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i2 + i3 = if_ (1)

il + i_4 = if_ (2)

il - 13 = ia_ (3)

Ü - 14 = ia_ (4)

The following equations can be derived from equations (1) and (3) as well as equations (1) and (4):

i ¹ + A ² ^ iL + liL ·· ( ⁵ )

A ³ + I ⁴ - Ά. - ia_ ........ (β)

Since the rectifier bridge circuits are symmetrical, the following applies: U = i _o and i - Λ _Λί so that the following relationships can in turn be derived from this

^ l = j2 = (tf_ + ia) / 2

Under this condition, the current (if + ia) / 2 flows to the rectifying elements D ₁ and D ₂ , while the current (if-ia) / 2 flows to the rectifying elements D ₃ and D ₄ (FIG. 3).

As already mentioned above, the field circuit and the armature circuit work independently of one another, the compensation current flowing to the field winding 6 as field current if and the current resulting from the control voltage e flowing to the armature 7 as armature current ia separately and independently of the field current. As a result, the servomotor works as a shunt motor. This operating state lasts until the rectifying elements D ₃ and D _{4 become} ineffective

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or the current ia becomes equal to the current if as a result of the increase in the control voltage e. At this point in time, the current (if-ia) / 2 flowing to the rectifying elements D ″ and D _{4 becomes zero, so that these rectifying elements D ″ and D 4 become} ineffective. The current (if + ia) / 2 flowing to the rectifying elements D- and Dg is also equal to the current ia and thus also to the current if. As soon as iä same if. is, the control voltage e, the field winding 6, the compensation voltage source and the armature 7 are connected in series with the bridge circuit 1, so that a current of the same magnitude flows through this circuit. The servomotor then works as a series motor.

In the embodiment described above, the rectifier circuit is 2 a rectifier bridge circuit on the field side. Instead of this, however, a single-phase half-wave rectifier circuit can also be used, consisting of a transformer T and a rectifying element D (Fig. 4), a single-phase full-wave rectifier circuit, consisting of a transformer T and the rectifying elements D shown in Fig. 5 or a three-phase full-wave rectifier circuit, consisting of six alignment elements ί (Fig. 6). When the rectifier circuit 2 on the field side a single-phase circuit according to FIGS. 4 and 5 or a triple-phase circuit according to FIG. 6 or even a multi-phase rectifier circuit in general, must (. generally the voltage source used for compensation be an AC power source. If, however, the rectifying circuit is a bridge circuit as shown in FIG. 1, can this voltage source supply both direct and alternating current.

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If the compensation voltage source is "its direct current", the rectifying circuit 2 can thereby entails. ; aö man the direct current source is connected directly in series with the direct current side of the bridge circuit 1 or by that one connects the positive terminal to the point P and the negative terminal to one end of the field winding 6. For this reason the circuit part designated 8 in the drawings can be used as a compensation direct current source for supplying the field winding β with direct current through the direct current side of the bridge circuit to be viewed as.

When the control voltage e is applied between the terminals 4 and 5 so that the terminal 5 is positive, the current flows to the field winding 6 always in the same direction and only the armature current changes its direction, whereby the operation of the Servo motor can be changed.

To the effect of the motor circuit according to the invention fully To shed light on, the following test results with the circuit according to the invention, which are achieved on a servomotor were explained in more detail. These results are explained in the form of graphs according to FIGS. 7-10. The one in the The servomotor used in experiments is a series servomotor with a nominal voltage of 1000 volts and a nominal current of 0.35 amps, a nominal power of 10 watts and a speed of 4000 rpm.

Fig. 7 shows the voltage characteristics when starting without load of the servomotor, which with the! Compensations-

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circuit is provided. In this figure are the results of the tests carried out with respect to different voltages when starting the engine, which were measured by gradually increasing the control voltage e. Of the. Compensation current (if) (A) has been used as a parameter. From Fig. 7 it can be seen that the starting voltage e without load is around 17 volts when there is no compensation current if flowing. This case corresponds to a conventional series servo motor. It can also be seen that the starting voltage is lowered to 4 volts without a load when a compensation current of 0.2 amps (about 57% of the nominal value) flows.

8 shows the voltage-speed characteristic of the servomotor with the compensation circuit according to the invention. That’s in there Speed ω as a function of the control voltage e with the compensation current if plotted as a parameter for operation without a load. If the compensation current if is 0.175 amperes, the straight line a applies, if = 0.35 amperes the straight line b applies and at if = 0 the straight line c applies. From this it can be deduced that the voltage at which the servomotor can start is the lower, the higher the compensation current. In other words, this means that by increasing the compensation current, the length of time that elapses before the servo motor responds to the applied voltage. However, exist for that The level of the compensation current insofar as certain restrictions are avoided as an excessive temperature rise in the motor got to.

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Fig. 9 shows the speed-torque characteristics of the servo motor with a compensation circuit according to the invention. There the torque τ is a function of the speed ω plotted using the compensation current if as a parameter for a control voltage e of 50 volts. If the Compensation current if 0.1 amps, curve a applies, curve b applies to if = 0.2 amperes, curve d applies to if = 0. It can be seen that the motor develops a series characteristic * when the load is high, whereas it develops a

Shunt characteristic shows when the load is low.

10 shows the armature current ia, the field current if and the speed ω, plotted over time t, a control voltage e of 50 volts being assumed. The solid curves show the values that are obtained when no compensation current flows. The dashed curves indicate the values that are obtained when a compensation current of 175 milliamperes flows. From the illustrations it can be seen that the response is greatly enhanced when the expansion joint) tion current flows.

The above description shows that by the invention Compensation circuit for a series servo motor, the servo motor can be given different excitation characteristics can. The motor can thereby automatically be influenced by a bypass characteristic switch to a series connection or vice versa. A number of advantages can be achieved thereby. In the first place it should be mentioned that this removes the ineffective range of the applied voltage-speed characteristic

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can be reduced considerably. Since the servomotor continues to have a bypass characteristic when the control voltage (power) is low it develops a high torque and starts even when the applied voltage is low. Another The advantage is that one and the same motor has both shunt and series characteristics and that of one is automatically passed over to the other. For example, if this engine is in a closed loop system is used, then this property enables the motor as a series motor in the event of large fluctuations in the control system to let it work and to use it as a shunt motor when there are minor fluctuations in the system based on the fact that in general the applied to the servomotor Voltage increases when there are large fluctuations in the control system occur, although this largely depends on the load.

Another advantage of the compensation circuit according to the invention is that the necessary for starting the motor Voltage can be lowered and the response of the motor improves. Because the compensation current in the field winding constantly generates a magnetic flux, both the response characteristics and the start-up characteristics of the motor are improved.

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Claims (1)

Claim Compensation circuit for a series servo motor for Improvement of the starting characteristics, characterized in that the field winding (6) of the motor is on the direct current side a rectifier bridge circuit (1,2) with a compensation current source is connected so that a current (if) constantly flows in the field winding (6), and that the armature (7) of the motor in series with the AC side of the rectifier bridge circuit (1, 2) is connected and forms a series circuit to which a control voltage (e) is applied.